Measuring system



M. E. LEEDS IHASURING SYSTEI Feb. 1a, 193s.

2 Sheets-Sheet 1 Filed Dec. 2 1952 u ya 1 a iQ u .01 @gamas` un 4.v ,IR5....6 fr: \.2 u

...null` IIIJI' My invention relates to electrical Patented Feb. N18,

UNITED l STATI-:s

PATENT oFFicEl Morris E.

riassume, srs'rsn ma., Philadelphia, n.; mmm to Leeds Northrop Company,Philadelphia, Pa., Pennsylvania a corporation of Application December z,193s, serial No. 645,333 l s 'cm-m (cl. 111-95) measuring andparticularly to arrangements for recording and/,or controlling chemical,physical, electrical and other conditions.

Heretofore in measuring systems, as recording 5 potentiometer systems,for example, batteries have methods -and systems hereinafter describedand been used to supply the measuring circuit, requiring care andreplacement of the batteries and frequent checking against a standardcell for recalibration of the system.

In accordance with my invention, a. current or voltage suitable forprecise measurements is derived from a commercial source of current,with high constancy of magnitude of the derived current notwithstandingthe usual and substantialfluctuations ofthe commercial source.

My invention also comprehends the various claimed. I For anunderstanding of my invention, and for illustration of variousembodiments thereof, reference is to be had to the accompanying draw`ings, in which:

Fig. 1 illustrates, diagrammaticallv, a recording system utilizing theinvention.

Fig. 2 illustrates a modification of the invention.

Pigs. 3 to 6 illustrate other modiiications.

'Fig-'l shows curves referred to'in explanation o f Figs. 3 to 6. A

. Referring to Pig. 1, the network P is illustrative of a potentiometernetwork, which for purpose of explaining one application of theinvention, is utilised to measure'and record the voltage and variationsin 'voltage of the thermocouple'T,

- the magnitude of the voltage varying in accordancewith the conditionunder measurementas temperature, turbidity, smoke density, etc.`

The voltage developed by the thermocouple is balanced against a voltagein the potentiometer circuit which is adjusted by relative movement` ofthe slide wire S and its contact Sc until there is no'defiection ofgalvanometer A. Speciiically, in the automatic recording system shown,which utilizes apparatus of the type disclosed in my Patent No.1,125,699 the disc i is rotated in one direction or the other, upondeflection of the needle,

scale. y y The readings taken or record made are notf until balance iseifected. AThe marker or pen 2 is driven from the shaft 3 carryingl disci so thatA it indicatesand records the variations on -chart C which isprovided with a suitable graduated accurate unless the current throughthe slidewires is maintained constant at the magnitude or value forwhich the instrument was calibrated.

` Heretofore batteries, primary orsecondary, have I apparatus. It didnot eliminate the need for attending to the'batteries and theirreplacement.

Previously, it has not been considered feasible to use commercialsources of current, as the usual power or lighting circuits, because thechanges 2o in current through the potentiometer slide wire A,duetoiiuctuations ofthesourcearisingfrom vary-v ing load conditions,poor regulation, etc.. would produce voltage changes of the order of thechangestobe'recordedormeasured. Inaccordancewithmyinventlon.themeasuringcircuitderivesitscurrentfromacommercial source, and notwithstandingthe usual and substantial variations ofthe commercial source, the

current through the potentiometer slide wire. or

equivalent. remains constant, or in any event a 'varieswithin suchnarrow limitsthat it does not precludehighlyaccuratemeasurements.

ThemotorMisenergizedfromtheline-IL from a commercial source of current.either direct or alternating. The speed ofthe motor is held constant bya suitable high-precision governor mechanism l, whichmay hfor example begenerally of the type shown in my Patent No. 1,476,824. BriefLv thesupport l rotated by the o motor M carries a centrifugal member C whichfor -speed in excess of -a magnitude predetermined by adjustment orselection of spring 'I, moves to separate contacts 8, l andso reduce orcut oil the current to the motor. In operatiomr the contacts 8, lrapidly separate and reclose holding the motor speed constant at thedesired l value despite substantial uctuations in voltage of the supplyline L, L. For example, the lineA voltage may vary as much as from 100to 120 50 vvolts and notwithstanding the substantial variation involtage, the speedv of motor M is held constant within narrow limits,as'for example` .1%.

Motor M is utilized to drive a slnall generator G; as indicated, thearmature il of the generator maybe mounted upon the shaftof motor M. Thefield excitation is preferably constant and therefore convenientlyprovided by the permanent neldl magnet II. Equivalent arrangements mayoi' course be used to provide field excitation. For clarity, thedisclosure is diagrammatic and hence the usual pole-pieces, supports,etc., have been omitted.

The generator brushes I2, I2 are connected to the terminals I3, Il ofthe potentiometer circuit by conductors I5, II which in accordance withprior practice would be connected to batteries. As the speed of thegenerator armature is held constant, the voltage it impresses uponterminal I3, Il remains constant and therefore the current through theslide wire is the same regardless of substantial iluctuations of voltageof line L, L. 'lhere is no longer need for batteries, standard cell.battery-current regulating resistance, etc., and the readings arealwavs' accurate whereas with batteries the accuracy fell ai: betweensuccessive checkings and recalibraons. v

Further to insure high constancy of voltage appliedto orcurrentthroughtheslidewire, there is included in series with the generatorarmature, resistor R whose resistanceis high compared to thesum total ofanyvvariationsinresistancein the system including the armature winding,and the various elements of the pontiometer system. Accordingly, thegenerator Gis constructed or operatedtoproduceavolta'geatitsbmshes whichis substantially higher than the voltage required at the potentiometerterminals.

'Ihe relatively high value of resistor R minimizestheeffectoi'anyvarlationinresistancebetweenthebrushesIZandthearmaturecommutator II, it also renders insubstantlal the effectof temperature upon the resistance of the armature winding. or upon thecold-junction compensatingresistor I3,insofarasitaectstheslide wirecurrent.

Withtheexception ofll,theotherresistorsof the system i. e., slidewire S,end coils Il-II. resistance2l,andresistorR,areoianalloy,as manganin",having a negligible temperature coeiiicientofresistance.

Thearmature Ilmaybewoundwithcoppercondulctonbecauseanychangeinoutputdueto`v2IIa1-erespectively,100|),18,2l),iland2,ohms;the

voltage dierence between I3 and I4 remains I22 millivolts, even thoughthe voltage oi' the supply source varies as much as 210%, and foralLiisual variations of temperature ofthe atmosphere.

Asthecunent-mthesudewireususnyneedonlybeasmallfractionoi'anampere,forexam ple, 5 milliamperes, the motorM-and generator G selfbalancing action of the system and moves therecorder pen.

In the modication shown in Fig. 2, motor MI is connected to a commercialsource of current L, L. Its speed may be held constant by a suitablegovernor, as in the system of Flg. 1, or if the source L, L suppliesalternating current at reasonably constant frequency, the motor can beof the induction type or of the synchronous type, without a governor.The motor M is utilized to drive the rotor IIIA of an alternator. Asshown, the rotor may comprise a non-magnetic disc with magnetic elements2I spaced peripheral- 1y thereof to comprise the rotor of aninductoralternator.

The field may be furnished by afpermanent magnet Ila, which isassociated with the shunt yoke 22 on which is disposed the inductor coil23. There is preferably provided a small, adjustable air gap between.yoke 22 and held magnet Ila.

An alternating voltage is generated in coil 23 as the result of thevarying reluctance of the magnetic circuit caused by rotation of discIla with its armature elements 2 I. If motor M is provided with agovernor, or if it is of the synchronous type, the generated voltage isconstant notwithstanding fluctuations of voltage of the commercialsource of supply.` If the frequency of the source changes, the speed oi'synchronous motor MI will change and consequently the` voltage across 23will change but this is compensated for, by arrangements hereinafterdescribedfor the usual variations of frequency of modern commercialsources of alternating current. When the motor M is of the inductiontype, the voltage across 23 is compensated for both change o1 frequencyand voltage of source L, L. A

To minimize the ellect of imperfect governing of motor M, or lack ofconstancy of frequency and/or voltage of the source L, L, there isprovided a. shunt circuit including resistance 2l in series with acapacity 25. The voltage induced in coil 23 and the frequency of thatvoltage both -vary directly with the speed ofmotor M. Ii' the frequencyincreases because of ln'crease in'speed of motor M, for any reason, thereactance of condenser 25 is less and consequently more current flowsthrough the shunt circuit, increasing the load on the generator G andcausing its voltage to drop.. Conversely, if the frequency decreases,less current iiows through the shunt circuit and the voltage acrossconductors I5, I6 increases. Consequently, the output voltage is heldconstant by the compensating network despite variations of the rotorspeed. 'n

As for measurement of direct current voltages,

the current through the potentiometer P should" be direct current, asuitable rectiiier 26 is interposed in circuit between generator GI -andthe measuring network. As shown the rectiier elements, preferably of thecopper-oxide type, or equivalent, may be arranged in bridge form. Ineffect, the rectiiler 26 performs the functions of the commutator ofgeneratorvG of Fig. 1.

To minimize the effect of change of resistance of the rectiiier withtemperature, there is provided resistor RI of resistance which is highcompared to any change in the resistance of the rectier. In general,resistor RI serves the same purposesastheresistorRoithesystemofFig. 1.

'Ihe output terminals of the rectifier are connected to thepotentiometer P. The responsive element TI, may be a, thermocouple, inFig 1, an

ion-concentration cell as indicated, or any other element suitable forthe particular conditions of measurement. This system like the system ofFig. 1, provides for supply of constant current or ,voltage to ameasuring circuit from a commercial source, obviatins the need forbatteries and attendant disadvantages.

characteristic in the supply of constantcurrent 1 to a measuringcircuit, device, or the like, the terminals of the transformer secondary2`| are connected through a lamp 28. or other device, having theaforesaid volt-ampere characteristic and a resistance 29of the usualtype whose characteristic 0D, Fig. 7 is linear throughout. The device Pis connected between neutral tap of the winding 21 and the commonconnection .of lamp 28 and resistance 29. Clearly, the current flowingthrough P isequal to the diii'erence between the currents drawn by theresistor 29 and lamp.

Resistor 29 is chosen so that its resistance is equal to the slope ofthe linear portion of the characteristic curve of lamp 28. i. e., sothat its curve OD is parallel to thelinear portion AB of curve OAB. The'diii'erence in current iiowing through P, if the resistance of P isnegligible is represented by the horizontal distance between f thecurves, and is therefore constant for all values of current lying withinthe range of thelamp characteristic.

-Regardless of the chosen value of tlxed resistance of P, the' currentthrough it remains constant so long `as the lamp isv operated over thelinear portion oi its characteristic curve'. trom .which it follows that4for substantial variation in voltage of the commercial source of supplyL, L. the current [through P remains constant, the simultaneous increaseor decrease of current within the zone AB. Fig. 7 being without eifectupon the current difference.

Fig. 4 is an elaboration of the fundamental circuit of Fig. 3 foradapting it for measurement of small direct currents by thepotentiometer method. As in Fig. 2, a rectifier 26 is interposed be-'tween the source of constant voltage and the' measuring' circuit P. Ininitially setting up the installation, the resistance 29 is adjusteduntil the current in the potentiometer does not vary for substantialchange in voltage of the supply L, L, and then resistance I0 is adjusteduntil the current through the .potentiometer corresponds to that forwhich it is calibrated The system is then in condition for operationwithout need for frequent checking, etc., as was necessary withbatteries.

The arrangement shown in Fig. 5 also /aiords constant current throughthe measuring circuit leg P of the network. As shown, it is'suitable foruse with a commercial source of direct current, and may be'us'ed with acommercial source of alternating current without 'need for a transformerwith split secondary. In the latter case, for direct currentmeasurements, a recti'er should be used generally as shown in Fig. 4;for alternating current measurements, an alternating currentgalvanometeris used. In both cases, the current through the measuring circuit assupplied by the commercial source of cin'rent remains constant so longas the lamps 2l, 28a are operated on the linear portions of theircharacteristics and provided that the resistance of the associatedresistorsn, 29a is equal to the slopes of the portions AB of the curv'esof the lamps.

Fig. 6 is similar to Fig. 5 except that lamp 28a is replaced by anotherresistor 29h. It is suited for both alternating and direct currentsources of supply subject to the same conditions as Fig. 5.

An instrument or system exemplied by either Fig. 5 'o'r Fig. 6 mayinclude rectlfying means, generically in accord with Fig. 4 o'rotherwise, and

so be utilizable for measurements of or in terms ot direct current orvoltage, whether the source of current connected to L, L be alternatingor unidirectional. The presence of the rectifying means when a direct oruni-directional source is employed renders its poling a matter ofindifference; without the rectifying means, Figs. 5 or 6,'a particularpoling of a direct or uni-directional source is essential, as indicatedby the (or markings.

The arrangementsoi Figs. 3 (4)-, 5 and 6 aord dierent values of currentbetween the points X-Y. as indicated by the formule below:

Fi! 3 (4) IR i-current through? R+2r Ie-zero intercept of lamp current(0C oi y lfm-1) rig. s fr R-mlmm urn-71? or Fig. 1

' l r-resistance between X-Y (through P) ICR s "am stant notwithstandingsubstantial variation in voltage of said commercial sourcel and thelchanges in magnitude of a condition under measurement, and balancing avoltage produced independently of said current and varying in accordancewith changes in magnitude of said condition against a voltage ofconstant magnitude produced in said measuring circuit by said derivedcurrent.

2. In the art of potentiometric measurements, the method of producing apotentiometer current oi constant magnitude which comprises driving amotor-generator from a commercial power line. maintaining the outputvoltage oi said generator substantially constant notwithstandingsubstantial variations in voltage of said line, impressing the generatorvoltage upon apotentiometer circuit whose resistance isconstantirrespective oi' the magnitude'of current traversing it, and balancing avoltage varying in accordance with .a condition under measurementagainst a voltage in said potentiometer circuit produced by tiow of thegenerator current therein.

3. In the art of potentiometric measurements, the method of producing apotentiometer current of constant magnitude which comprises driving amotor-generator-from a commercial power line, maintaining the outputvoltage of said generator substantially constant notwithstandingsubstantial variations in voltage oi' said line and variations inmagnitude of the condition under measurement, and impressing thegenerator voltage upon the potentiometer circuit through resistance ofmagnitude which is substantially constant and high relative to anyvariations in resistance A relative to any incidental variation inresistance of said circuit due to change of temperature or othercondition of operation.

5. AIn the art of potentiometric measurement, the method of producing apotentiometric current of constant magnitude which comprises deriving adirect current voltage from a commercial source oi current, maintainingthe magnitude oi said voltage substantially constant notwithstandingsubstantial variation in voltage of said commercial source andvariations in magnitude of the condition under measurement, producing bysaid derived voltage iiow of current vthrough a path including in seriesa measuring circuit of substantially constant resistance and resistancewhose magnitude is substantially constant and high relative to anychange in the resistance of said path due to change of tempera- 'ture orother condition ot operation.

6. In the art of potentiometric measurement,

the method of producing a potentiometric current of constant magnitudewhich comprises deriving from a commercial source of current a- 7. Ameasuring system comprising a meas` uring 'circuit of substantiallyconstant resistance, a commercial source of current subject tosubstantial voltage variations, means for deriving a direct currentvoltage from said source and impressing it upon said measuring circuitincluding means for maintaining the magnitude of said derived voltagesubstantially constant, and resistance in series with said circuit ofmagnitude which is substantially constant despite variations oftemperature and high relative to any incidental variations in resistanceoi' said circuit.

8. A measuring system comprising a measuring circuit,'a commercialsource 'oi' current, a motor energized therefrom, a generator driven bysaid motor and supplying current to said measuring circuit, andresistance in circuit between said generator and said measuring circuitof magnitude which is substantially constant and high relative to anyincidental variation o! resistance of said circuit due to change oftemperature or other operating condition.

MORRIS E. LEEDS.

